The research objective of this proposal is to test the functional cooperativity of the common gamma chain (IL2RG) and the LIM-Only 2 (LMO2) oncogene in leukemia induction. The proposal builds upon the Pi's postdoctoral work where retroviral insertional mutagenesis models were used to show that H2rg is a frequent site of insertion in Lmo2-induced T-cell leukemias. The results provide genetic evidence for cooperativity between these two genes and suggest an explanation for the high incidence of leukemia in the French gene therapy trial of X-linked severe combined immunodeficiency (SCID-X). The model suggests that the affected patients developed leukemia because of two "hits", insertional activation of LMO2 by the gene therapy vector and constitutive expression of the IL2RG transgene. The following specific aims will formally test this concept: (l)Transgenic mice overexpressing IL2RG will be constructed and followed for the development of leukemia;(2) IL2RG transgenics will be interbred with Cd2-Lmo2 transgenic mice to make bitransgenic mice overexpressing both genes. These mice will be followed and monitored for disease and compared with single transgenic littermate controls. Lmo2 transgenic mice develop T-cell leukemia with a median latency of 200 days, and so doubly transgenic mice, overexpressing both Lmo2 and IL2RG genes would be predicted to develop disease with shorter latency and/or higher incidence;and (3) genes within the IL2RG pathway will be tested for their ability to cooperate with Lmo2 in leukemia induction. StatSb transgenic mice will be interbred with Cd2-l_mo2 transgenics to create bitransgenics to be monitored as in Aim 2;and, cooperativity with constitutively active JAK3 will be explored using retroviral transduction of bone marrow. Confirmation of Lmo2/ll2rg cooperativity in gene therapy-induced leukemias has broad implications for the field of gene therapy, the treatment of SCID-X, and also the pathogenesis of sporadic T-cell leukemia. This Mentored Clinical Scientist Development Award will give the Principal Investigator protected time to pursue this important research and establish a foundation for an independent and productive career in academic Hematology. (End of Abstract)